1. Field of the Invention
This invention relates to fluid flow control and metering, and more specifically relates to a fluid flow switching system that employs a photodetector and light source to provide a system sensitive to flow.
2. Background Information
The invention disclosed herein is an improvement to the flow switch disclosed and described in U.S. Pat. No. 5,021,619 issued Jun. 4, 1991 to the inventor of the invention disclosed herein and is incorporated herein by reference. This prior patent essentially shows a cantilevered flat flow sensing spring blade disposed to extend into the flow of a fluid through a container, pipe, tube, duct, etc. which produces a drag force on a target blade, displacing it in a downstream direction. The fluid flowing through the pipe bends the spring until it comes to rest against a hollow support tube that is located just downstream of the spring. The support tube holds the spring steady; thus, protecting it from excessive vibration induced by turbulent fluid flow plus static loads due to steady state fluid flow loads.
In the prior patent referred to hereinabove, a magnet on the flow sensing spring blade activates a reed switch inside the support tube. Fluid flow acting on the spring blade moves the magnet toward the support tube thereby, indicating a certain level of flow. The triggering fluid flow rate can be determined by adjusting the size, shape and stiffness of the spring blade.
However, magnetically operated reed switches have an inherent hysteresis. As the magnet approaches the reed switch at some point, the magnet is attracted to the switch by magnetic field coupling and quickly moves the last bit of distance to the support tube under the influence of the magnetic force alone, rather than because of force of the fluid flow against the flow target's spring blade which thus, introduces some error in the flow measurement.
An additional mechanical hysteresis effect is present in the reed switch itself, which once closed, tends to latch in the closed position via non-linear magnetic attraction. Therefore, as the fluid flow declines, the reed switch will remain latched closed until the external magnetic coupling force effecting the reed switch is no longer sufficient to maintain the latched condition and the reed switch contact open. Thus, the fluid flow rate, when the switch opens, is somewhat below the fluid flow rate at which the switch closes (a hysteresis effect). This hysteresis effect or gap is again, in many situations, a useful feature in that it prevents the switch from oscillating (i.e., chattering on and off) when the fluid flow happens to be right at the triggering point. In effect, the double magnetic latch/unlatch hysteresis of the magnet and reed switch internal blades creates a fluid flow hysteresis dead band, which reduces flow measuring sensitivity. The magnetic hysteresis system and thus, the flow turbulence hysteresis system is completely determined by local magnetic fields of the magnet/reed switch combination, which is an artifact of each particular magnet/reed combination that cannot be adjusted except by changing one or both members.
A further improved system, to reduce this hysteresis effect is disclosed and described in U.S. patent application Ser. No. 08/736,050. In this improved fluid flow switch and metering system, the reed switch is replaced with a Hall Effect transducer which has greater sensitivity than a reed switch and provides an output depending upon the magnetic force applied to it by a magnet. In this patent application various configuration and combinations of magnets, including various materials are disclosed, that effect the output of the Hall Effect transducer. Substantial improvement in the sensitivity and reduction in the hysteresis makes this system useful in many applications. However, even greater sensitivity, particularly a low flow rate is needed.
Fluid flow devices having a light detecting device are known in the art. One such device is shown in U.S. Pat. No. 4,945,344 of Farrell et al. In this patent, an electro-optical slide has a reflector that reflects light from a light source to a detector. This device employs a complicated arm having a ball bearing and spring mounted on a rubber boot that allows the vein to be deflected by fluid flow. The device disclosed in the Farrell Patent is not versatile or sensitive enough for most applications as the detection mode is separated from the optics. The device has a seal or boot around the arm makes this device sensitive to fluid pressure. Further, the friction of the ball detent in the flow sensitive arm would make this device unworkable at low flow rates. There are additional defects in the window and the slide mechanism. If the seal is not fluid tight the window will quickly become contaminated and the slide will fail or stick. Further there is no convenient way to clean the window. At best, this device may only be used as an on/off indicator.
Another patent that uses a light source and photo detector for determining fluid flow as it flows is disclosed in U.S. Pat. No. 4,958,144 of Greiss. The device disclosed in the Greiss patent needs a heavy seal which eliminates the possibility of any useful sensitivity except as an on/off indicator. Further, the heavy seal means this device is very pressure dependent. Also, the large vane, heavy seal separating the optics, and spring loaded sensor mechanism means this device is not very sensitive to flow. It is a simple on/off device. Another disadvantage is the large vane that is necessary as this device needs a big target. The large vane can completely choke off or block flow. Both patents cited above suffer from low turn down ratios (i.e., the ratio of maximum allowable flow rate divided by the minimum detectable flow rate) on the order of ten (10) or less.
Another object of the present invention is to provide a flow metering and switching system having a turn down ratio (i.e., maximum flow/minimum detected flow=turndown) on the order of one hundred (100+) or more.
Therefore, it is one object of this invention to employ a non-magnetic optical micro-sensor transmitter receiver pair operating in both transmissive and reflective modes thereby, totally eliminating the use of magnetics and associated magnetic hysteresis effects.
Yet another object of the present invention is to employ a non-magnetic optical micro-sensor transmitter receiver pair that provides a very narrow on/off flow switch operating band thus, providing an extremely sensitive flow measurement device, which is precisely repeatable and essentially free of meaningful. hysteresis.
Still another object of the present invention is to provide a flow metering and switching system employing a photo detector and a light beam interrupter that has a variety of characteristics. The radiation beam source and photo detector combination can be broad spectrum from x-ray to ultraviolet, to visible to infrared and beyond, depending upon each particular situation.
Still another object of the present invention is to provide a flow metering and switching system in which the flow is determined by blocking or interrupting the path of light between a source and a photo detector.
Yet another object of the present invention is to provide a flow metering and switching system in which a blocking or interrupting mechanism is provided via a fluid flow sensing bending beam to selectively control the interruption of light between a source and a photo detector.
Yet another object of the present invention is to provide a flow metering and switching system having a blade mounted on a fluid flow sensing bending beam that selectively blocks the path of light from a source to a photo detector.
Yet another object of the present invention is to provide a flow metering and switching system in which the flow sensing blade is an opaque member that blocks the transmission of light from the source to a photo detector.
Still another object of the present invention is to provide a flow metering and switching system in which the blade mounting on a flow sensing bending beam has a varying opacity to gradually diminish the light transmitted from a source to a photo detector.
Yet another object of the present invention is to provide a flow metering and switching system in which a reflective surface is mounted on a flow sensing bending beam to control or reflect light from a source to a photo detector.
Still another object of the present invention is to provide a flow metering and switching system having a means to block the light flowing from a light source to a photo detector in which the light source is a LED optical disc transmitter and the photo detector receiver is an optical disc receiver.
Yet another object of the present invention is to use a variety of blocking or interrupting devices to vary the relative light received by a photo detecting device.
Still another object of the present invention is to tire an interrupting blade having a male shaped blocking configuration.
Yet another object of the present invention is to provide a flow control, or flow metering switching have a female shaped blocking blade configuration for varying the light between a source and a photo detector.
Still another object of the present invention is to use a variety of reflective surfaces to vary the quantity of light received by a photo detecting device from a light source. These blocking blades could have a surface that is partially reflecting, and partially non-reflecting. In some cases, the reflecting areas may be separated by an oblique line providing a triangular reflective surface and a triangular non-reflective surface. In another embodiment, the reflective surface would be one-half of a square or rectangle, while the non-reflecting surface would cover the other half.
Yet another object of the present invention is to provide a selective radiation absorption flow sensing blade having a varying opacity from clear to completely opaque. The flow sensing blade would be clear at a forward edge and would become increasingly opaque toward a rear edge until it was completely opaque to the light source or vice versa.
Another object of the present invention is to provide a flow switch and meter that has improved sensitivity by measuring the variation in light detected by a photo detector caused by fluid flow vortex shedding at, or down stream of the flow of a flow sensitive bending beam.
Yet another object of the present invention is to provide a flow switch and meter that includes appendages on a bending beam to enhance the vortex shedding to further improve sensitivity.